Switching converter with wide input voltage range and control circuit thereof

Abstract

A switching converter includes a first and second switch pair, an inductor, a first and second error amplifying circuit, a control voltage generator, and a pulse width modulation circuit. The first error amplifying circuit provides a first error amplifying signal based upon an output feedback signal representative of an output voltage and an output reference signal. The second error amplifying circuit provides a second error amplifying signal based upon the first error amplifying signal and a current sense signal representative of a current flowing through the inductor. The control voltage generator provides a control voltage based upon a voltage difference between the second error amplifying signal and a reference voltage. The pulse width modulation circuit provides a first pulse width modulation signal to control the first switch pair and a second pulse width modulation signal to control the second switch pair, based upon an input voltage, the output voltage and the control voltage.

What is claimed is: 
     
         1 . A switching converter comprising: 
 a first switch pair configured to be coupled in series between an input voltage and a reference ground, for selectively coupling a first terminal of an inductor to the input voltage or the reference ground;   a second switch pair configured to be coupled in series between an output voltage and the reference ground, for selectively coupling a second terminal of the inductor to the output voltage or the reference ground;   a first error amplifying circuit configured to receive an output feedback signal representative of the output voltage and to provide a first error amplifying signal based upon the output feedback signal and an output reference signal;   a second error amplifying circuit configured to receive the first error amplifying signal and a current sense signal representative of a current flowing through the inductor, and to provide a second error amplifying signal based upon the first error amplifying signal and the current sense signal;   a control voltage generator having a first input terminal to receive the second error amplifying signal and a second input terminal to receive a reference voltage, wherein the control voltage generator is configured to provide a control voltage based upon a voltage difference between the second error amplifying signal and the reference voltage; and    a pulse width modulation circuit configured to provide a first pulse width modulation signal for controlling the first switch pair and a second pulse width modulation signal for controlling the second switch pair, based upon the input voltage, the output voltage and the control voltage.   
     
     
         2 . The switching converter of  claim 1 , wherein the pulse width modulation circuit comprises: 
 a first comparison circuit having a first input terminal to receive a first modulation signal and a second input terminal to receive a first ramp signal representative of the input voltage, wherein the first comparison circuit compares the first modulation signal with the first ramp signal and provides a first comparison signal;   a second comparison circuit having a first input terminal to receive a second modulation signal and a second input terminal to receive a second ramp signal representative of the output voltage, wherein the second comparison circuit compares the second modulation signal with the second ramp signal and provides a second comparison signal;   a switching cycle control circuit configured to provide a switching cycle control signal;   a first logic circuit configured to provide the first pulse width modulation signal based upon the first comparison signal, the switching cycle control signal and the second pulse width modulation signal; and   a second logic circuit configured to provide the second pulse width modulation signal based upon the second comparison signal, the switching cycle control signal and the first pulse width modulation signal.   
     
     
         3 . The switching converter of  claim 2 , wherein: 
 the first modulation signal is a sum signal of the control voltage and a first voltage dividing signal representative of the output voltage;    the second modulation signal is a difference signal provided by subtracting the control voltage from a second voltage dividing signal representative of the input voltage; and   the switching cycle control signal is provided in response to the first ramp signal increasing to the second voltage dividing signal.   
     
     
         4 . The switching converter of  claim 2 , further comprising: 
 a first ramp signal generator configured to provide the first ramp signal, comprising: 
 a first capacitor; 
 a first current source configured to provide a first charging current for charging the first capacitor, wherein the first charging current is proportional to the input voltage; and 
 a first discharge switch configured to discharge the first capacitor in response to the switching cycle control signal; and 
 a second ramp signal generator configured to provide the second ramp signal, comprising: 
 a second capacitor; 
 a second current source configured to provide a second charging current for charging a second capacitor, wherein the second charging current is proportional to the output voltage; and 
 a second discharge switch configured to discharge the second capacitor in response to the switching cycle control signal. 
 
   
     
     
         5 . The switching converter of  claim 2 , wherein the first ramp signal, the second ramp signal and the switching cycle control signal are in phase. 
     
     
         6 . The switching converter of  claim 1 , wherein: 
 the first pulse width modulation signal and the second pulse width modulation signal are paused in response to the first error amplifying signal decreasing to be less than a first threshold voltage; and   the first pulse width modulation signal and the second pulse width modulation signal are transmitted to the first switch pair and the second switch pair for a conversion process in response to the first error amplifying signal increasing to higher than the first threshold voltage.   
     
     
         7 . The switching converter of  claim 6 , further comprising: 
 a control switch coupled between the first input terminal and the second input terminal of the control voltage generator, wherein the control switch is turned on when the first error amplifying signal is less than the first threshold voltage, and the control switch is turned off when the first error amplifying signal is higher than the first threshold voltage.   
     
     
         8 . A control circuit for a switching converter, comprising: 
 a first error amplifying circuit configured to receive an output feedback signal representative of an output voltage of the switching converter and to provide a first error amplifying signal based upon the output feedback signal and an output reference signal;   a second error amplifying circuit configured to receive the first error amplifying signal and a current sense signal representative of a current flowing through an inductor of the switching converter, and to provide a second error amplifying signal based upon the first error amplifying signal and the current sense signal;   a control voltage generator having a first input terminal configured to receive the second error amplifying signal and a second input terminal configured to receive a reference voltage, wherein the control voltage generator is configured to provide a control voltage based upon a voltage difference between the second error amplifying signal and the reference voltage; and   a pulse width modulation circuit configured to provide a first pulse width modulation signal and a second pulse width modulation signal based upon an input voltage, the output voltage and the control voltage, wherein the first pulse width modulation signal is used to control a first switch pair of the switching converter for selectively coupling a first terminal of the inductor to the input voltage or a reference ground of the switching converter, and the second pulse width modulation signal is used to control a second switch pair of the switching converter for selectively coupling a second terminal of the inductor to the output voltage or the reference ground.   
     
     
         9 . The control circuit of  claim 8 , wherein the pulse width modulation circuit comprising: 
 a first comparison circuit having a first input terminal to receive a first modulation signal, a second input terminal to receive a first ramp signal representative of the input voltage, the first comparison circuit compares the first modulation signal with the first ramp signal and provides a first comparison signal;   a second comparison circuit having a first input terminal to receive a second modulation signal, a second input terminal to receive a second ramp signal representative of the output voltage, the second comparison circuit compares the second modulation signal with the second ramp signal and provides a second comparison signal;   a switching cycle control circuit configured to provide a switching cycle control signal;   a first logic circuit configured to provide the first pulse width modulation signal based upon the first comparison signal, the switching cycle control signal and the second pulse width modulation signal; and   a second logic circuit configured to provide the second pulse width modulation signal based upon the second comparison signal, the switching cycle control signal and the first pulse width modulation signal.   
     
     
         10 . The control circuit of  claim 9 , wherein: 
 the first modulation signal is a sum signal of the control voltage and a first voltage dividing signal representative of the output voltage;    the second modulation signal is a difference signal provided by subtracting the control voltage from a second voltage dividing signal representative of the input voltage; and   the switching cycle control signal with a first type transition edge is provided in response to the first ramp signal increasing to the second voltage dividing signal.   
     
     
         11 . The control circuit of  claim 9 , further comprising: 
 a first ramp signal generator configured to provide the first ramp signal, comprising: 
 a first current source configured to provide a first charging current being in a first proportion to the input voltage for charging a first capacitor; and 
 a first discharge switch configured to discharge the first capacitor in response to a first type transition edge of the switching cycle control signal; and 
 a second ramp signal generator configured to provide the second ramp signal, comprising: 
 a second current source configured to provide a second charging current being in the first proportion to the output voltage for charging a second capacitor; and 
 a second discharge switch configured to discharge the second capacitor in response to the first type transition edge of the switching cycle control signal. 
 
   
     
     
         12 . The control circuit of  claim 9 , wherein the first ramp signal, the second ramp signal and the switching cycle control signal are in phase. 
     
     
         13 . The control circuit of  claim 8 , wherein: 
 the control voltage becomes zero in response to the first error amplifying signal decreasing to less than a first threshold voltage; and   the control voltage starts to change from zero in response to the first error amplifying signal increasing to higher than the first threshold voltage.   
     
     
         14 . The control circuit of  claim 13 , further comprising: 
 a control switch coupled between the first input terminal and the second input terminal of the control voltage generator and configured to being controlled by a clamp control signal, wherein the control switch is turned on when the clamp control signal indicates that the first error amplifying signal is less than the first threshold voltage, and the control switch is turned off when the clamp control signal indicates that the first error amplifying signal is higher than the first threshold voltage.   
     
     
         15 . A control circuit for a switching converter, wherein: 
 the control circuit switches between a first mode and a second mode when an input voltage approaches an output voltage, wherein in the first mode, during one switching cycle, a first terminal of an inductor of the switching converter is selectively coupled to the input voltage or a reference ground and a voltage at a second terminal of the inductor is substantially equal to the output voltage, and in the second mode, during one switching cycle, a voltage at the first terminal of the inductor is substantially equal to the input voltage and the second terminal of the inductor is selectively coupled to the output voltage or the reference ground.   
     
     
         16 . The control circuit of  claim 15 , further comprising: 
 a first error amplifying circuit configured to receive an output feedback signal representative of the output voltage and to provide a first error amplifying signal based upon the output feedback signal and an output reference signal;   a second error amplifying circuit configured to receive the first error amplifying signal and a current sense signal representative of a current flowing through the inductor, and to provide a second error amplifying signal based upon the first error amplifying signal and the current sense signal;   a control voltage generator having a first input terminal configured to receive the second error amplifying signal and a second input terminal configured to receive a reference voltage, wherein the control voltage generator is configured to provide a control voltage based upon a voltage difference between the second error amplifying signal and the reference voltage; and   a pulse width modulation circuit configured to provide a first pulse width modulation signal and a second pulse width modulation signal based upon the input voltage, the output voltage and the control voltage, wherein the first pulse width modulation signal is used to control a first switch pair of the switching converter, and the second pulse width modulation signal is used to control a second switch pair of the switching converter.   
     
     
         17 . The control circuit of  claim 16 , wherein the pulse width modulation circuit comprises: 
 a first comparison circuit having a first input terminal to receive a first modulation signal and a second input terminal to receive a first ramp signal representative of the input voltage, wherein the first comparison circuit compares the first modulation signal with the first ramp signal and provides a first comparison signal;   a second comparison circuit having a first input terminal to receive a second modulation signal and a second input terminal to receive a second ramp signal representative of the output voltage, wherein the second comparison circuit compares the second modulation signal with the second ramp signal and provides a second comparison signal;   a switching cycle control circuit configured to provide a switching cycle control signal;   a first logic circuit configured to provide the first pulse width modulation signal based upon the first comparison signal, the switching cycle control signal and the second pulse width modulation signal; and   a second logic circuit configured to provide the second pulse width modulation signal based upon the second comparison signal, the switching cycle control signal and the first pulse width modulation signal.   
     
     
         18 . The control circuit of  claim 17 , wherein: 
 the first modulation signal is a sum signal of the control voltage and a first voltage dividing signal representative of the output voltage;    the second modulation signal is a difference signal provided by subtracting the control voltage from a second voltage dividing signal representative of the input voltage; and   the switching cycle control signal with a first type transition edge is provided in response to the first ramp signal increasing to the second voltage dividing signal.   
     
     
         19 . The control circuit of  claim 17 , wherein the first ramp signal, the second ramp signal and the switching cycle control signal are in phase. 
     
     
         20 . The control circuit of  claim 16 , wherein: 
 the control voltage becomes zero in response to the first error amplifying signal decreasing to less than a first threshold voltage; and   the control voltage starts to change from zero in response to the first error amplifying signal increasing to higher than the first threshold voltage.